High intrinsic noise and absence of hysteresis in superconducting quantum interference devices with large Steward-McCumber parameter

We investigated niobium thin film superconducting quantum interference devices (SQUIDs) with large Steward-McCumber parameter (βc > 1). No hysteresis was observed in the current-voltage (I-V) characteristics of the SQUIDs, even for βc ≈ 17. We attribute the absence of hysteresis to an excess voltage noise of the junctions which increases the SQUID intrinsic noise δΦs. It can be represented by an effective noise temperature T* of the SQUID which is higher than the bath temperature T. We simulated SQUID I-V characteristics using the measured device parameters and confirmed the absence of hysteresis.